# CVE-2026-97040: Cgo directive injection via .syso files disguised as Go object files in cmd/go and cmd/link


- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** ALPINE-CVE-2026-97040, DEBIAN-CVE-2026-97040, GHSA-9767-p5x8-v2p2, GO-2026-6851, UBUNTU-CVE-2026-97040

## What is CVE-2026-97040?

CVE-2026-97040 is a vulnerability in cmd/go, published on 11 Nov 2026. 

### Official description

Building a package containing a crafted ".syso" file could bypass cgo flag validation and inject arbitrary linker flags when linking. When loading ".syso" entries from a package archive, the linker only checked for recognized host object headers (ELF, Mach-O, PE, and XCOFF) before falling through to Go object parsing. A ".syso" file beginning with a "go object" header was parsed as a Go compiler object, allowing untrusted cgo metadata directives (such as "cgo_ldflag" or "cgo_dynamic_linker") embedded in the ".syso" file to be passed to the external linker without validation. Additionally, ".syso" filenames longer than 16 bytes lost their ".syso" extension when truncated in archive headers, and unrecognized ".syso" formats forced external linking in pure-Go builds. The linker now rejects ".syso" files that are not recognized host object formats, and "cmd/go" and "cmd/pack" preserve the ".syso" suffix when truncating long archive member names.

## Which versions are affected by CVE-2026-97040?

1 open source package ship an affected version, including toolchain.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `toolchain` | Go | All versions | 1.26.11, 1.27.4 |

## How do I fix CVE-2026-97040?

Upgrade toolchain to a fixed version for your release line: 1.26.11 or 1.27.4.

## Is CVE-2026-97040 being exploited?

There is no known exploitation of CVE-2026-97040 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97040 and fix it if it is affected.

What it is: CVE-2026-97040 is a vulnerability in cmd/go, published on 11 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-97040 in the wild and no public exploit code.

Affected packages and fixed versions:
- toolchain (Go): affected all versions; fixed in 1.26.11, 1.27.4

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-97040/ (Markdown: https://insights.sbomify.com/CVE-2026-97040/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97040
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97040
- OSV: https://osv.dev/vulnerability/CVE-2026-97040

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97040/
Summaries are generated and may contain mistakes; the official description above is the record.